1. Field of the Invention
This invention relates to the technology of metal deposition and to the consolidation, during the process of deposition, of the metal deposited. It relates especially to the production of metal by physical vapour deposition (as hereinafter defined) but has application also to the production of metal by spray deposition.
2. Discussion of Prior Art
Unconventional alloys produced by rapid solidification processing exhibit significant improvements in individual properties over alloys produced by the conventional, ingot metallurgy, routes. Aluminium alloys prepared by rapid solidification are being developed for aerospace applications. Most of the techniques for the manufacture of rapidly solidifed alloys involve the production of powder by atomization or by splat quenching. The production of bulk aluminium alloys prepared by these processes is complicated by the problems of degassing and consolidating the material.
Physical vapour deposition is a process in which an alloy is formed by evaporation of constituents followed by direct condensation from the vapour upon a temperature controlled collector. Physical vapour deposition should not be confused with chemical vapour deposition--the latter being characterised by the production of a deposit through chemical reaction in the vapour phase and such is absent in physical vapour deposition. Physical vapour deposition is an alternative to conventional rapid solidification processing for the synthesis of metastable alloys, in which full advantage can be taken of both the exceptionally effective quench obtained by deposition on an atomic scale and the suitability of bulk condensates for direct conversion to wrought forms.
A process of physical vapour deposition (hereinafter abbreviated to "vapour deposition") is described in depth in the Applicant's prior patent No. GB 1521293, and the current specification does not attempt to provide a description to the same depth save in aspects directly relating to the invention hereinafter disclosed. That prior specification documents the need for a vapour deposited metal to be mechanically worked during the process of deposition for the creation of a suitable microstructure and for the avoidance of porosity. In that document various forms of mechanical working are disclosed, the preferred form being a peening action such as that produced by mechanically driven hammers or flails. However, rolling is also disclosed as a potentially effective alternative. In a vapour deposition process the mechanical working is not required to provide consolidation in the sense that consolidation is required for powder compaction. It is found that in vapour deposition that porosity is caused by surface effects such as shadowing caused mainly by the protuberences that develop on the surface. In a vapour deposition process the degree of mechanical working or consolidation should be sufficient to remove asperities from the surface between each exposure to the vapour flux in order to avoid shadowing, and sufficient also to provide a suitable laminar microstructure. Excessive mechanical working may adversely affect the properties exhibited by the product material.
In spray deposition processes a similar requirement for deposit consolidation can be evident. In spray deposition processes a molten metal or alloy is atomised in an inert atmosphere to give a spray of liquid particles which are directed on to a cooler surface where they impinge, coalesce and solidify. Certain spray deposition processes are applied to the production of thin sheet or a coating layer and in such process consolidation of the deposit is unlikely to be required. Other spray deposition processes involving a high density of spray are effectively self-consolidating by virtue of the impact of sprayed particles. However, there can be advantage in operating a spray deposition process at a spray density less than that which is self consolidating because by doing so the problems of producing sufficient rate of cooling to retain metastable phases are reduced. In such circumstances some means of imposed mechanical consolidation may be required and one prior art process utilising such is that known as simultaneous spray peening. This process utilises a peening produced by projecting peening shot through the spray of metal droplets onto the deposit. Obviously there could be scope for alternative arrangements producing the same in-situ and in-process mechanical working.